Audi 100 overheats...

Hi! Must try this forum for help. My 1992 100 2.8 q is making trouble. It overheats. I have change all that can be changed but it still gets hot. I have also bleed it in all possible ways. The fans dont kick in but they work when i hot wire them.
My last tought is the head gasket but it have no signs og such i can see. It sems like the water flow, sirculation is bad.
Any ideas?

Could be that thermo switch in the radiator is defective..could be a blocked radiator..could be several issues including a thermostat. If the radiator is blocked..the upper radiator hose will be hot and the lower hose cold..that could be a defective thermostat too. How old is the radiator? Is the thermostat new? OEM? There is a lot of junk parts out there. Hard to do a diagnosis over the net with little information.

Hi! Thank you for answering Rusty! The radiator, termoswitch, thermostat, waterpump and the multiswitch was new i july this year. I also took out the waterpump and thermostat to inspect it last week.
I suspect this problem came when i replaced the G62 and air got in the system. The engine runs great, no smoke, no oil in water and no water in oil. Strange.
I took it for a test drive friday and tought i solved it. All was fine for 15 mins but down a steep hill the temp climb to about 110 degrees. The fan works when hot wiring but did not came on

The fansnot coming on when hot sounds like your problem. When you say "hot wired" the fan switch..did you bridge the connector when the thermo switch plugs into? If so..do you have two speeds? Will the fans come on with the A/C on?

Here is a link that talks about checking the fan switch. It is in the most part applicable to your car. You may not have some S6 parts like the after-run relay..or maybe you do.

Hi! I am greatfull for your help.
Yes the fan works at both speeds when i bridge the connectors. And no it wont come on when i turn on the ac.
I must find out where that power comes from. Is it the multiswitch?
And they should kick in about 90-95 degrees?

If the fan works when you bridge the thermo switch..then the 12v power, grounds, resistor plate and relays are working. Sounds like a bad thermo switch or the radiator (plugged up) is not allowing hot coolant to run over the switch. Could be air in the block too. That keeps the coolant from flowing. If you confident the radiator is good..get a new thermo switch. Get a Wahler 251959481K which is a slightly cooler 87/76- 93/82 switch. The original switch is part number 191959481A 95/85-102/92 and is NLA.

The fans should come on with the A/C on..you need to investigate that problem..probably just a relay.

Thanks a lot! Been out now. Its snow and on summer tires i did not drive far but the car ran for about 30 min at idle. I also res it up for a long time. The temp was steady at 90gC. I did bridge the fans in second speed. The termoswitch is new so that is strange. I will buy i new one like the one you recomend.

After another test drive today, iím pretty convinced that the head gasket must be blown. The car act normal for a while, but it seems like the pressure is building up in the cooling system after a while.
So then i just have to do the jobb. But is it a change that the engine block also can have a crack or it that not so common? Its a AAH engine.
I thought about machining the heads and do all the gaskets.

I will try that Thanks. This problem is driving me crazy. After bleeding the car yesterday, it worked all right for about 20 min exept from, ill think, the hot air in the cabin disapered driving Down hill. It came back drivin up hill.